Your little swimmers need more than fast food and a case of beer to keep them in top shape. What you eat and drink, and even how much you exercise, can affect your ability to have children. Two handfuls of walnuts a day, though, could give your sperm the boost they need to get the job done.

Walnuts are a natural source of omega-3 fatty acids that, along with other polyunsaturated fatty acids, are needed for sperm to mature and work properly. Other foods, like fish oil and flaxseeds, also contain these compounds, but walnuts come in a convenient snack-and-go format.

In a recent study, published in the Biology of Reproduction, researchers from the University of California tested the ability of walnuts to keep sperm happy, healthy, and on the go.

After 12 weeks, men who ate 75 grams of walnuts a day—about two-and-a-half servings—had higher levels of both omega-6 and omega-3 fatty acids in their blood. Their sperm also reaped the benefits, with improved swimming ability, size, and shape.

Men in the study who skipped the walnuts—and actually avoided eating any tree nuts during the 12 weeks—didn’t see a boost in the health of their sperm.

Future research will be needed to show whether walnuts can work as a treatment for male infertility. In the meantime, if you’re expecting your partner to be expecting, keep your little swimmers swimming with a couple of handfuls of walnuts.